At present, electric automobile is not an unfamiliar term. It prevails over internal combustion automobile with the obvious advantages in the aspect of pollution and noise, which has been contributed to the rapid development. The electric automobile is powered by the large storage battery, thus technology for charging the storage battery is crucial. Because of the lower power and undemanding requirement of charging rate, the general household charger usually has a longer charging duration and is inapplicable for the electric automobile. Commercial charger for the electric automobile must feature less battery loss and pollution and high rate. The large storage battery used by the electric automobile has high capacity and power and long service life. Thus, its charger, especially the commercial charging equipment equivalent to the fuelling station for the internal combustion automobile, requires very high power as such charging equipment will charge all storage batteries of one or even more automobiles rather than only one battery. However, blindly increasing the power of the charging equipment will exert considerable influence on the power grid in the course of use and high power is the main factor affecting the power grid.
The traditional powerful charging equipment is designed based on the phase-controlled rectification technology and uses the thyristor as power device. In addition the general three phase rectification technology for charger, such charging equipment also develop the multi-wave charger, but the charger based on the phase-controlled rectification technology is heavy with low power factor and more harmonic pollution. The charger with lower power factor will have a great effect on the power grid and other electrical appliances when the charge is increasingly loaded. To solve the problems in aspects of the power factor and harmonic pollution, such phase-controlled charger must be equipped with the proper devices for harmonic suppression and reactive power compensation which will increase the size of equipment and cost. However, these measures still can not solve the described problems basically.
Just as filling the internal combustion automobile, charging the electric automobile can be completed in around ten minutes normally. For the on-board charger of the electric automobile, the storage battery can be charged wherever there is the power outlet available, but has limited power handling capacity as it is subject to the space on the automobile. It can only provide slow charging with little current and has long duration of charging. When using the traditional charging technology, the duration for charging the storage battery of the electric automobile may be 12 hours at least. Besides, the traditional charging mode is too simple which may shorten the service life of the storage battery. It can be said charging the electric automobile with traditional technology simply could not be popularized.
Consequently, it is necessary to develop a fast charging system with high power factor and low harmonic and free from devices for harmonic suppression and reactive power compensation.